I was facing a similar issue as mentioned by you. I do not know if it is a known defect or what. I tried a lot many time but still the form opens in a Best Practice view. When I checked from developer studio I found that there is no classic form available for work order. WOI:WorkOrder form is having two views 1. Simplified User View and 2. Default User view. and the default view for this form is "Simplified user View which I changed from
Choose the default view as "Default User View" and not a simplified user view.
Now you would be able to see the form in classic view kinda.
But it will be for all the users as the view is changed at form level.
May be it is defect. I am using SRM 7.6.04 SP2 version.